Discharge lamp manufacture



June 30,1959

H.v D. FRASER DISCHARGE' LAMP MANUFACTURE iled Jan. 3L 1955 Exif/9057'INVENTOR. #.P. F'iewsE/e. 5% 9* 4%@ HWEA/E'Y United States Patent2,892,665 DISCHARGE LAMP MANUFACTURE Hugh D. Fraser, West Caldwell, NJ.,assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application January 31, 1955, Serial No.485,218 4 Claims. (Cl. S16- 26) This invention relates to discharge lampmanufacture, and has to do more particularly with the introduction ofmercury into discharge lamps especially of the highintensity orhigh-pressure type having quartz envelopes.

Basically, the invention proposes novel means and method ofincorporating the precise amount of mercury individually into a lamp sosaid lamp will have predetermined exact operating characteristics.

Likewise broadly considered, the invention contemplates operationalsteps .and apparatus repetitiously usable on successive lamps withfacility and ease.

An important object of the invention is to permit nal sealing of thelamp to be deferred with a considerable time lapse after the lamp hasbeen charged with its proper amount of mercury.

Other objects, advantages and novel features of construction andpmethodwill appear to persons skilled in the art to which the inventionappertains as the description proceeds, both by direct recitationthereof and by mplication from the context.

Referring to the accompanying drawing in which like numerals ofreference indicate similar parts throughout the several views;

Figure 1 is an elevational view of the discharge lamp as it appears onthe exhaust machine ready for the initial seal-olf of the tubulation;

Figure 2 is a view of the initially sealed-off lamp, inverted fromposition shown in Fig. 1 for introduction of the mercury into the lampenvelope, ready for second sealing of the tubulation;

Figure 3 is another elevation of the lamp located in apparatus by whichprecise amount of mercury is determined for retention in the lampenvelope;

Figure 4 is a graph of the are voltage during operation in the apparatusof Figure 3; and

Figure 5 is a view of a part of the showing of Figure 3 indicating thedischarge as discontinued and the mercury required for the same ascondensed in the envelope and the excess condensed in the tubulation.

The lamp, as herein illustrated, is an elongated tubular quartz envelope11, closed at both ends with the closures supporting main electrodes 12,13 respectively within end regions of the hollow of the envelope and oneclosure also supporting an auxiliary electrode 14 in the envelope.Intermediate of the ends of the envelope of the lamp in its embryonicstage is a laterally projecting tubulation 15, which, in the completedlamp, is tipped off proximate to the envelope wall as indicated bydotted lines 16 in Fig. 5. Tubulation 15 is used, first, to connect theenvelope to an exhaust machine 17 to evacuate the envelope, after whichargon or other suitable gas is introduced through said tubulation intothe envelope. I employ a usual construction of exhaust machine whichreceives the lower end of the tubulation depending from the lampenvelope. ln the tubulation is a capsule 18, upwardly open, whichcontains liquid mercury 19 retained therein by gravity. The capsule 18is retained in tubulation 15 by group consisting of thon'a and zirconia.

a spring clip (as shown inFig. 1) and a necked-down 1 2,892,665 PatentedJune 30, 1959 ice ` and thereafter the tubulation is initiallysealed-off at 20 by gas llame 21 at a location below the capsule 18. Thelamp is then inverted, as shown in Fig. 2, so that tubulation projectsupwardly from the lamp envelope and permits the mercury 19 to drop tothe bottom of the envelope, where it splatters, forming a lot of smallerdrops on the enevelope Wall. The tubulation is then sealed olf a secondtime, fas at 22 by gas flame 23, between the envelope and capsule.

In order to assure full discharge or gravitation of the mercury from thecapsule into the lamp envelope, the mercury drop may be coated with a lmof oxide of the The application of such oxide may be made directly onthe drop of mercury prior to introducing it into the capsule or into thetubulation, or may be applied by dusting the iinely powdered refractoryoxide on the interior of the capsule or on the interior of thetubulation. By any one of these expedients, the mercury is kept fromadhering to the tubulation so that all of the mercury will pass into theenvelope when the lamp is inverted for that purpose as above described.The amount of mercury is in excess of the quantity ultimately requiredfor proper operation of the lamp, but the excess will be eliminated inaccordance with the process described hereinbelow.

Upon again inverting the lamp as in Fig. 3, it is brought to a supportedhorizontal position on rack cleats 24 xed at the upper side of aheat-resisting table 25, said table having a hole 26 therein properlylocated to receive the tubulation therethrough. At the underside of thetable coaxial with said hole 26, is a heating coil 27 through which thetubulation is inserted. The coil is shorter than said tubulation wherebythe lower sealed end portion 22 of the tubulation projects from thelower end of the coil. This projection of the end of the tubulation isfor purpose of enabling the same to be cooler than the main body of thetubulation so that mercury may condense gradually therein.

The electrodes, as Well as said coil 27, are connected to an electricsource and a discharge will thereby be instigated and maintained withinthe envelope. The discharge creates heat in addition to the heatdeveloped by said coil, and the mercury in the envelope vaporizes.Consequential upon such vaporization of the mercury, the pressure in theenvelope increases to a maximum for the amount Vof mercury present, andthis maximum is intentionally greater than that desired for normaloperation of the lamp. In order to conserve the heat and obtain fullvaporization of the mercury, a cozy or hood 28 is applied over the lampwhile being thus processed. The amount of heat developed by coil 27 maybe adjusted by a rheostat 29 or other current controlling mechanism inthe electrical circuit to the coil.

Mercury vapor of course lls the tubulation as well as the envelope, andsince the lower end of the tubulation is relatively cool, the mercurywill gradually condense thereat, thereby reducing the pressure. As thedischarge voltage across the electrodes depends directly upon mercuryvapor pressure in the envelope, reduction of the pressure reduces thedischarge voltage to substantially the desired equilibrium value. Therate of the reduction of pressure can be controlled by adjustment of thecurrent supply heating the tubulation by coil 27, and when the dischargevoltage reaches the aforesaid equilibrium value, the current and heatingare discontinued. The voltage values may be observed on a voltmeter 30connected across the lines supplying equilibrium voltage, that is, thevoltage at which the lamp is intended to function in use, is designatedas volts. In practice, it

has been found that this equilibrium or operating voltage is slightlylower than the value at which the discharge voltage and heating arediscontinued. The discharge or arc voltage during` fabrication of thelamp is indicated by solid line graphv 3-1 of Fig. 4, the dischargestarting at A at about eighteen volts and mounting, in the exampieshown, toa maximum of about 175 volts at B, and then dropping' back to145 volts at C where heating and discharge voltage for fabricationpurposes are discontinued. The operating voltage of the finished lamp isdesignated by broken line graph 32 of Fig. 4 and shown as leveled oi at'D. Since heating coil 27 and hood 28 are not used with the completedlamp, the warm-up period is slightly longer than during fabrication, butas the mercury has been reduced in the finished lamp from the amountoriginally in the envelope during fabrication, the operating voltagelevels off. at substantially l40 volts in the illustrated embodiment.

During fabrication, immediately upon discontinuance of theY arc voltageand heating-coil current, a cooling stream, preferably air, isdirectedagainst a lower part of the envelope at a distance from the tubulation.lt is a characteristic of mercury vapor, that it will condense at a coolspot. Consequently substantially all of the vapor isV converted toliquid state at-33, Fig'. 5, in a restricted area of the envelopeimmediately adjacent to an air-jet tube 34 shown terminating close tothe envelope near one end thereof. rlThe tiltedl downwardly away fromcondensed mercury 33 does not enter the tubulation and mix with thecondensed portion 3S or mercury' that has collected in the bottom ofsaid tubulation. At any convenient time thereafter, the tubulation issealed at le proximate tothe envelope, thus removing the condensedmercury 3S of the tubulation and leaving only the condensed mercury 33remaining in the envelope. The pressure in the completedy lamp, when thelamp is not in operation, isv usually less than one atmosphere, but withthe lamp in operation, the-pressure created by the vaporization of themercuryV may riseto several atmospheres.

Illustrative of controlling mechanism for fabrication purposes, l haveindicated feed lines 56 (Fig. 3), from the usual alternating currentcommercial supply. These feed lines energize the primary 37 ofv atransformer the secondary 38 of which supplies energy to the electrodesthrough switches 40, 41. Those lines also supply energy through twoother switches 42, 43, one of which, as 42, is in` serieswith asolenoid' coil 44 the core 4S of which is operatively connected to anair valve 46 for tube 34, and another one, as 43, closes the heatingcoil circuit. These several switches are operated in unison, forinstance by a magnet 47 to simultaneously open switches 40, 41 and 43 tothe electrodes and to the heating coil and to close the switch 42. tothe air valve solenoid 44'; Circuit to magnet 47 is appropriatelymanipulated automatically or by the operato-r to thus operate the bankof switches 40, 4l, 42 and 43 when the arc voltage, as indicated byvol'tmeter 39, has dropped back to the desired or appropriate level orreading. Current to the magnet may be reduced in voltage by interposinga transformer 48 in the circuit thereto from the line, and anoperator-controlled switch 49 is shown in the primary line of thattransformer.

The'fabrication operations, in brief, include sealing o the tubulationthree times, irst an initial seal-olf at 2i@ beyond'capsule i8, thenafter the envelope has been inverted, a second seal-off at 22 betweenthe envelope and capsule, and ultimately a nal seal-off contiguous tothe envelope, as at 16, after the mercury content has been vaporized andsegregated with the desired condensation thereof in the envelope and theexcess in the portion of the tubulation beyond thenal seal-off. Thisseparate condensation of the needed mercury to remain in the lamp andthe excess mercury to be excluded' avoids necessityj of making the finalseal at the moment that the vapor the tubulation so that the envelope iskept level or I pressure is at its current value. Instead, I am enabledto delay the 'dnalseal-olf indefinitely and still have proper amount ofmercury and vapor pressure for operation of the lamp after the envelopeis ultimately sealed-olf. While the circuit shown is advantageous forcommercial fabrication of lamps, it will be understood that the switchescontrolling the arc current andthe heating coil current may be handoperated and likewise the air valve is operable by hand and I have mademany lar'nps utilizing such hand operations.

I claim:

l. The method of introducing mercury into an arc tube in an amountcorresponding to that required to produce a mercuryLvapor' pressurewithin said arc tube which mercury-vapor pressure corresponds` to apredetermined arc tube operating voltage, comprising exhausting said arctube through an elongated tubulation, introducing into said arc tubethrough `said tubulation a predetermined pressure" of inert ionizablegas and an excess of mercury over that desired, tipping off saidelongated tubulation' at a point considerably removed from' said arctube, positioning' said tubulation soV that it is substantially belowsaid arc' tube, operating an electric discharge within said arc tube tocause same to heatV and' vaporize the mercury therein, the operatingelectric discharge within said arc tube having an operating potentialwhich is" proportional to the pressure of mercury vapor therein,maintaining the lowermost portion of said tubulation at a' tentperaturesubstantially lower than the temperature of the operating' arc tube tocause some of thc mercury vapor formed by the heat of the operating arctube to' condense therein, applying heat to said' tubulationintermediatev the ends thereof to limit and control the rate of mercurycondensationvin the cooler lowermost portion of said tubulation,de-energiing the electric discharge within said arc tube and withdrawingsaid applied heat' from said tubulation" when the operating voltage ofsaid discharge has reduced to a predetermined value, cooling a portionof thestill-hot arc tube which is lowermos't and removed from saidtubulation to condense on said cooled arc tube portion the desiredamount of mercury now present in" said arc tube and to rapidly` drop themercuryvapor pressure in said arc tube to less than atmospheric', andthereafter tipping on said tubulation at a pointv con# tiguous tos'aid'arc tube.

2. The method of processing a mercury-discharge device having anenvelope' charged with an excess of; mer? cury over the amount needed,said envelope having an elongated tubulation opening therein, and saidtubulation having a sealed end portion considerably removed from saidenvelope, which method comprises vaporizing said mercury in saidenvelope by heat appliedrelative to said envelope, condensing theexcesspart of said vaporized mercury in said tubulation proximate thesealed end portion thereof in addition to heating another portion ofsaid tubulation by a separate controlled source'of heat to control therate of mercury condensation in said tubulation, condensing the neededpart of said mercury in a portion of said envelope away from saidtubulation, and sealing-off from said envelope vsaid tubulationcontaining said excess condensed mercury thereby isolating the same fromsaid envelope.

3. The method of processing a mercury-discharge device having anenvelope vcharged with an excessv of mercury over the amount needed,said envelope having an elongated tubulation opening therein, and saidtubulation having a sealed end portion considerably removed from saidenvelope, which method comprises vaporizing said mercury in saidenvelope by heat applied relative toV said envelope, condensing theexcess part of said mercury' in said tubulation proximate the sealed endportionA thereof in addition to heating another portion of saidtubulation by a separate controlled source of heat to' control the rateof mercury condensation in said tubulation, cooling a limited area 0fSaid' envelope away from said tubulation to condense the needed part ofsaid mercury thereat for retention in said envelope, and sealing-olffrom said envelope said tubulation containing said excess condensedmercury thereby isolating the same from said envelope.

4. The method of processing a mercury-discharge device having anenvelope charged with an excess of mercury over the amount needed, saidenvelope having an elongated tubulation opening therein, and saidtubulation having a sealed end portion considerably removed from saidenvelope, which method comprises vaporizing said mercury in saidenvelope by heat applied relative to said envelope, in addition heatinga portion of said tubulatio-n removed from the sealed end portionthereof by a separate controlled source of heat to vaporize mercury inthe heated portion of said tubulation, condensing vaporized mercuryproximate the sealed end portion of said tubulation, controlling theheating of said heated tubulation portion to Control mercurycondensation in said tubulation proximate the sealed end portionthereof, continuing to condense vaporized mercury in said tubulationproximate the sealed end portion thereof until excess mercury over theamount needed in said envelope is condensed in said tubulation, andsealing-off from said envelope said tubulation containing excessmercury.

References Cited in the le of this patent UNITED STATES PATENTS

